Studies have been conducted on the application of a polymer containing a silsesquioxane skeleton to various fields because the polymer has a specific skeleton structure. A polymer having a silsesquioxane skeleton structure has been heretofore synthesized by a sol-gel method involving the use of alkoxysilane such as triethoxysilane. However, the sol-gel method involves a large number of problems, for example, the method requires a long reaction time, makes it difficult to control a reaction, and is apt to leave fine holes.
Further, in recent years, a polymer using silsesquioxane having a cage-type structure or a derivative thereof has been studied, and the polymer is expected to have excellent weatherability, heat resistance, physical properties, and optical properties. For example, Lichtenhan et al. have disclosed a method of producing a copolymer obtained by polymerizing a silsesquioxane having a cage-type structure containing a defect, that is, a so-called incomplete cage-type structure (a structure which is not of a complete octahedral shape and part of which is lost) with siloxane (U.S. Pat. Nos. 5,412,053 and 5,589,562). The production method involves crosslinking the polyhedral oligomeric silsesquioxane by using a bifunctional silane, siloxane, or organometallic compound having amine etc. as a functional group. Lichtenhan et al. have also disclosed a method of producing a copolymer having, as its main chain, silsesquioxane of an incomplete cage-type structure bound with siloxane etc. and a method of producing a copolymer using silsesquioxane of a cage-type structure as a pendant copolymer component and methacrylic acid as a copolymer main chain component (Comments Inorg. Chem., 1995, 17 115-130). Further, Lichtenhan et al. also disclose a method of producing a silsesquioxane-siloxane copolymer by reacting —OH which is bound to Si at a corner of the incomplete cage-type silsesquioxane with, for example, bis(dimethylamino)silane (Macromolecules, 1993, 26 2141-2142). Anderson et al. have obtained a silsesquioxane oligomer by: lithiating a silsesquioxane having silanol with n-butyllithium; and reacting the resultant with a silsesquioxane having Si—Cl at one site in a perfect cage-type structure (Chem. Matter., 2006, 18(6) 1490-1497).
The inventors of the present invention have reported that a polysiloxane can be obtained from an organic silicon compound containing silanol and referred to as a double-decker structure alone or by reacting the compound with silane or siloxane having Si—Cl (WO 2005/000857). Further, the inventors have reported that a linear polymer having a perfect cage-type structure on its main chain can be obtained by reacting a silsesquioxane having two silanols at positions symmetric with respect to each other with a siloxane having Si—Cl (JP 2006-22207). These documents discloses a method of obtaining a polymer of a silsesquioxane, but these documents describe neither a compound corresponding to a polysiloxane containing a reactive group at a terminal of its polymer main chain to be provided by the present specification nor a method of producing the compound.